The present invention relates to vehicle seats and more particularly to an improved seat back for a vehicle front seat.
Seat structures in vehicles such as automobiles are required to meet federal safety standards. These standards are higher for front seat backs than rear seat backs in automobiles, because front seat backs have to be designed to withstand rear occupant impact and rear head form impact. Accordingly, most front seat backs are formed of stamped, die cast, or tubular steel or other metal constructions, although other materials such as expensive resins or composites having a high modulus of elastisity (rigidity) can be used. Such seats are necessarily relatively heavy and/or expensive.
The necessity for high structural strength is increased when seat belts are incorporated into the seat back structure. While most seat belt shoulder harnesses are anchored to the vehicle frame, it is desirable for a number of reasons to anchor the seat belt to the seat back itself. One reason is that the seat belts remain in adjustment when the seat position is changed. Such seat belts also provide an improved fit on the passenger and free the vehicle from design constraints required by placement of a seat belt retractor and "D" ring on the vehicle frame. However, anchoring a front seat shoulder harness on the seat back itself increases the structural requirements of the front seat back, because the front seat back then has to restrain the forward momentum of front seat passenger in an impact.
Because of the high strength requirements of front seat backs, particularly when the seat belt is anchored to the front seat back, front seat backs are usually formed of expensive high strength materials and tend to have a high mass.
Blow molding is a low cost plastic molding technique that has found wide applications in the formation of plastic beverage bottles from high density polyethylene ("HDPE"). The blow molding process involves inflating a heated hollow plastic blank in a closed mold. The process is desirable because it produces a lightweight closed section that has good structural characteristics. However, the normal blow molding process is limited to a maximum molding pressure of about one atmosphere (14.7 psi). This pressure restricts the materials that can be used to thermoplastic materials having a low modulus of elasticity (relatively elastic), such as polyolefins (e.g., HDPE), with low levels of fillers (15% or less) and glass reinforcements. Generally a material having a modulus of elasticity of 500,000 psi or less is considered a low modulus material. Materials with a higher modulus of elasticity, particularly a modulus of 1,000,000 psi or more, are considered high modulus materials. For example, an unfilled HDPE has a modulus of about 170,000 psi, while a filled HDPE has a modulus of about 400,000 psi.
Because of the strength limitations of such materials, the use of blow molding for seat components has been limited to components requiring little structural strength, such as seat pans and rear seat backs. This technique has not been applied to front seat backs.
An object of the present invention is to provide a lightweight, cost efficient front seat back comprising a blow molded thermoplastic body into which a reinforcing member is incorporated, wherein the seat structure complies with applicable safety standards and permits the affixation of a seat belt anchor directly to the seat back.